Propagation of potentiometric signals based on electric conduction of sea water

This research proposes a seawater wireless communication system that utilizes the electric conductivity in saltwater in a space electrically isolated from the open sea. An insulator (polyvinyl chloride) tube with a length of 1-25 meter was filled with an electrolyte solution to evaluate its characteristics based on electrolyte concentration. In 1 meter tube, the output signal was stronger with higher NaCl concentrations, and an output of 0.14 V was obtained with an input of 1 V voltage amplitude and 1MHz frequency for 3.5% NaCl(aq). An equivalent circuit of the experimental system using the polyvinyl chloride pipe was created, and a bandpass filter was designed using an inductor. As a result, with a frequency of 1.1 MHz and a voltage amplitude of 1 V, a 1 V output was successfully obtained. In a large area propagation, the signal characteristics were measured using an electrically seawater pool from the open sea with dimensions of 25 m×15 m ×0.9 m. Signals with a transmission range of 15 meters, input voltage of 50 V, and frequency of 5-10 MHz were able to be transmitted with a signal strength of -40 to -50 dB. Similarly, when an inductor was inserted as a bandpass filter, a signal with a strength of -25 dB, which was 33 dB greater than when no inductor was present, was transmitted at 1.5 MHz, which is enough for real-time video communication.